This invention relates to cardiac catheters of the type used to control a patient's heart activity by providing electrical pulses to the heart to pace the heart rhythm. The use of such catheters often may be required when heart rhythm malfunctions. By applying electrical pulses directly to the heart the rhythmic malfunction may be corrected, at least temporarily, to reestablish more regular heart activity and stabilize the patient in that condition. Such pacing techniques are used more commonly in emergency situations during post-operative care and in intensive care units for pre-operative as well as post-operative care.
Although a variety of catheters with pacing electrodes are available commercially and are in regular clinical use, they are not free from difficulty. For example, often it is important to establish electrical contact as quickly as possible, such as when trying to restore a functioning heartbeat to a patient under emergency conditions. The prior devices, however, have not lent themselves to rapid and accurate placement of the electrodes. In some techniques independent electrodes are placed separately through different veins to contact the atrium and ventricle. Other devices have bundled together a number of electrodes of different lengths arranged so that the longer electrodes will reach into the right ventricle while the shorter electrodes will reach into the right atrium.
Still other devices have been suggested, such as that in U.S. Pat. No. 3,949,757 to Sabel in which atrial and ventricular leads are contained within a sheath and in which the atrial lead is slidable with respect to the sheath so that it may be projected into surface contact with the atrium wall after the ventricular lead is placed. Although the device described in the Sabel patent appears to be more conveniently used than the prior devices, it nevertheless fails to overcome a number of remaining difficulties. For example, none of the prior devices, including Sabel, makes for any provision by which the wide variation in heart sizes of various patients may be accomodated. In this regard it is desirable, for a number of reasons, to place the electrode(s) in direct contact with the heart muscle. Moreover, it is desirable that certain regions of the ventricle and atrium (for example, the sino-atrial node) which are acutely sensitive to electrical stimulation, be contacted directly by the electrode. However, because of the wide variation, from patient to patient, of the size of the heart, no practical device has been proposed which was capable of quick and easy placement and adjustment so as to make direct contact with specific portions of the heart muscle, regardless of the size of the patient's heart.
It is desirable, when pacing a heart, to contact the most electrically sensitive areas (such as the sino-atrial node) because that enables lower energy pulses to be used. The use of lower energy pulses is desirable because it tends to create less interference and disruption with other electrically controlled functions of the heart. Until the present invention, precise and reliable placement of the leads in direct contact with selected portions of the heart could not be achieved reliably and, as a result, it often was necessary to apply relatively high energy pulses. Often the lead might not be in direct contact with the heart wall at all, much less in contact with a particularly sensitive portion of the heart wall. As a result, the higher energy pulse is necessary to overcome the impedance of the blood and the distance between the electrode and the heart wall. In addition, applying a high energy pulse also may interfere with the sensing function which often is desirable when pacing. Pacemaking equipment often includes sensing circuitry by which the electrical activity and condition of the heart may be monitored by the electrodes in the intervals between pacing pulses. The conditions sensed can be used to control the nature and timing of the pulses applied to the patient. If it is necessary to apply high energy pulses, as has been common with many of the prior devices, that tends to disrupt and interfere with the sensing function of the pacemaker.
Another important consideration in cardiac pacing is proper synchronization of atrial and ventricular functioning. Often it is desirable to pace the atrium and the ventricle in proper sequence so as to achieve as near as normal heart function as possible. This, in turn, may require placement of an electrode in each of the ventricle and the atrium and proper and precise control of the pulsing so that they operate in their normal sequence. In some types of rhythmic disorders, such as heart block, sequential pacing of both the atrium and ventricle is essential.
Still another difficulty presented with the prior art devices is the tendency for the electrode leads to become dislodged from their position in the heart as a result of the repeated flexing of the heart in its pumping action. Dislodgement or shifting of an electrode from its intended position disrupts the pulsing and/or sensing functions with potentially serious consequences.
It is among the primary objects of the invention to provide an atrio-ventricular pacing catheter which overcomes the foregoing and other difficulties.